(I) Field of the Invention
This invention relates to sulphur concrete compositions, to a method of forming articles therefrom, and to the articles so formed.
(II) Description of the Prior Art
Articles such as preformed concrete building blocks, roof and floor tiles, paving slabs, structural members and other articles have previously been formed from concrete comprised of a mixture of cement, such as hydraulic or Portland cement, mineral aggregate and water, plus various optional additives such as air entraining agents, water reducers, plasticizers, water-proofing and possibly others. These materials may in some instances be combined with reinforcement such as steel bars, wires or fibers. The materials are generally blended in a concrete mixer and the resultant wet mixture is placed and densified in a mold or form to produce a desired shape. Hydration of the cement paste then takes place over a period of time after which the mold or form is removed to form the article. Concrete formed in this manner has reasonable strength and durability in most environments except for severe freeze-thaw conditions and in the presence of certain chemicals such as road salts, industrial wastes, etc. In addition, the rising cost of Portland cement, its availability and the high use of energy to manufacture it have made its utilization less attractive for many applications.
Sulphur is readily available in many countries as a by-product of the oil and gas industry. The relatively low cost and unique properties of sulphur have led to its utilization as a construction material particularly to replace or extend the use of Portland cement or asphalt cement.
In British Pat. No. 1,884 there is described an artificial stone formed from a mixture of a cement such as Portland cement, mineral aggregate, clay, water and sulphur and U.S. Pat. No. 3,954,480, A. F. Inderwick, issued May 4, 1976, describes concretes formed from similar ingredients.
Sulphur concretes have also been developed in which elemental or modified sulphur completely replaces the Portland cement. Although this sulphur concrete has the advantage of rapid curing to a usable form by cooling, there are disadvantages in that all the ingredients of the mixture must be heated to about 150.degree. C. prior to and during mixing. Attendant with the requirement for special equipment and handling, many special molds are required since the molten mixture is very fluid. Further, there is the potential danger of workers being exposed to toxic gases during the mixing if the temperature of the sulphur is inadvertently raised too high.
A particular shortcoming of this approach is the high volume of shrinkage that occurs when the formed article cools to ambient temperature, often resulting in distortion as well as inaccurate final dimensions which is unacceptable in blocks used in a mortarless building system, which must be producible with accurate predetermined dimensions. In addition there is a tendency for the mineral aggregate to settle while the sulphur is molten and for segregation of the mineral aggregate and molten sulphur to occur during pouring of the hot mix. Finally the prior method necessitated cleaning of the mold in between the manufacture of each article, since part of the composition would stick to the mold surface after removal of the molded part.